The present invention generally relates to methods and systems for more accurately determining radar cross section (RCS) or location of an object reflecting radio frequency (RF) waves using true time delay of an optical signal. More specifically, time delay may be induced by, for example, interaction of the optical signal with receiving elements of an active electronically scanned array (AESA), such as patch antennas, bow tie antennas, or another antenna that uses a substrate acting as dialectic between a metal plate and a ground plane, see, e.g., FIG. 7.
Two approaches associated with scanning radar antennas include mechanical scanning and electronic scanning. Mechanical scanning requires that a whole antenna be mechanically positioned in azimuth and elevation in order to sweep a desired coverage area. Electronic scanning uses phase or frequency input to shift the beam in angle. Advantages of electronic scanning include multiple agile beams, which allows simultaneous tracking, searching, and communicating functions; no moving mechanical parts to fail for greater reliability; less space requirements; increased ease of upgrading the transmit/receive (T/R) modules; short pulses for low probability of interception; and ability to deal with high congestion spectrum environments (e.g., highways with large numbers of self-driving vehicles with radar systems that could jam each other).
Disadvantages of electronic scanning include beam squint; cooling requirements for the T/R modules; narrow field of view; and the cost is greater than a rotating antenna. Existing AESAs control amplitude and phase of each antenna element or group of antenna elements. Conditioning or manipulation of beam direction and shape allows for greater steer ability over conventional mechanically steered antennas. However, because of wide, instantaneous bandwidths of waveforms and narrow beam width, beam squint can be generated, and the resulting beam squint may be enough to steer off target. Many years of effort and millions of dollars have been expended in research and development to mitigate beam squint in phased array antennas. Thus, among other things, a need exists to mitigate beam squint and associated issues with front-end AESA components.
A developmental effort associated with various embodiments of the invention addresses several design or developmental challenges. A first challenge was to develop a receive antenna architecture that uses optical phase delay as the primary means of gathering information rather than traditional means of electrical signals. A second challenge was to develop a model and research materials for a receive element that will transform electrical signals into an optical phase delay.
An embodiment of the invention can include a phase delay element design that couples an electromagnetic field with an electromagnetic (EM) signal and uses an induced voltage to change an index of refraction for an electro-optic (EO) material that then induces a phase delay in the EM signal. The EO material can also function as a dielectric for the phase delay element. An optical signal can propagate through an exemplary phase delay element and be compared with a reference signal with no phase delay. The delayed EM signal may then be compared to the EM reference beam that does not undergo delay to determine the true time delay.
One new feature of one embodiment includes providing an ability to quickly transform an electrical signal into an optical signal. This conversion provides many advantages such as enabling true time delay between receive elements, thus mitigating the effects of beam squint; less electromagnetic interference (EMI); fewer microwave components in the receiving signal path; an ability to process signal remotely; less stringent power requirements at the antenna; and an ability to multiplex many signals onto one optical waveguide.
According to a further illustrative embodiment of the present disclosure, methods of manufacturing and use are also provided. Further illustrative embodiments can also include using optical phase delay produced from an alternative embodiment, which could be used to replace photodetectors. Another application can include remotely measuring EM fields. An example can include using an optical fiber placed along a parameter and integrating the antennas into the fiber, providing an ability to discern a location along the fiber line that an EM signal originates.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment exemplifying the best mode of carrying out the invention as presently perceived.